Radiation curable resins comprising hyperbranched polyesters

ABSTRACT

Hyperbranched polyester of a polyol with 3 to 10 reactive hydroxyl groups, preferably of equivalent reactivity, and an aromatic polycarboxylic anhydride with 2 to 4 carboxyl groups, preferably 3 carboxyl groups, each hydroxyl group of the polyol forming an ester linkage with one anhydride group of the polycarboxylic anhydride, and further glycidyl (meth)acrylate or allyl glycidyl ether forming ester linkages with the remaining carboxyl groups of the anhydride and free hydroxyl groups. Further in the hyperbranched polyester (meth)acrylic anhydride and/or an aliphatic carboxylic anhydride form ester linkages with the free hydroxyl groups. The invention also comprises a process for the production of hyperbranched polyesters and such polyesters obtainable by the process. The hyperbranched polyesters can be used as resins, curable by UV irradiation, for the production of coatings, adhesives, laminates, foils and thin films and fibre-reinforced composites.

The present invention relates to new hyperbranched polyesters and aprocess for the production thereof and curable resins comprising thepolyesters.

Radiation-curable resins are increasingly used in various industrialapplications, replacing conventional thermally cured and solvent basedcoatings and adhesives. The radiation-curable resins have favourableproperties, e.g., high speed and low energy consumption of cure,solvent-free formulations, room temperature operation and high qualityend-products. The principal components of a radiation-curable resin areoligomers (or prepolymers) and comonomers. The oligomers constitute thebackbone of the three-dimensional polymer network formed by curing.Important types of oligomers commonly used for coating are acrylatedepoxies, acrylated polyurethanes, unsaturated polyesters and acrylatedpolyesters (or polyethers) which give desired properties of the finalcured films. However, those oligomers usually consist of linearmolecular chains. The viscosity of the resin increases rapidly withincreasing chain length of the oligomer. To obtain an operationalviscosity of the formula for spraying, dipping, roll coating, etc.,large amounts of multifunctional comonomer are required for the primaryfunction of viscosity control. In addition, the comonomers haveimportant effects on the cure reaction and the properties of the finalproduct. Some of the comonomers have low cure rate, cause shrinkage ofthe film during curing, and have high costs and a limited shelf life.Multifunctional acrylates are the preferred monomers inradiation-curable systems because of their rapid curing rates and lowprices. The common acrylate monomers are volatile and toxic, and havestrong odour. Therefore, the trend is to use radiation-curable oligomerswith viscosity close to the required application viscosity in order toreduce or eliminate the use of comonomers.

An object of the present invention therefore was to obtain oligomerswith reduced viscosity compared to known oligomers with similarmolecular weight.

A further object of the invention was to present oligomers which inresin applications needs a lower amount of multifunctional comonomers ornone at all, while the resins still have a low viscosity, a high curerate, an acceptable degree of curing and the final products have goodmechanical properties.

A further object of the invention was to offer a process for theproduction of such oligomers.

The objects of the invention was solved by the hyperbranched polyester,the process for the production of these hyperbranched polyesters andresin comprising them, as claimed in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a reaction scheme for the synthesis of the hyperbranchedpolyester.

FIG.2 depicts an IR spectra of the products at different stages.

FIG. 3 depicts the molecular structure of the three polyester isomers.

FIG. 4 depicts an idealized formula of the hyperbranched methacrylatedpolyester with 8 double bonds.

FIG. 5 depicts an idealized formula of the hyperbranched methacrylatedpolyester with 16 double bonds.

FIG. 6 depicts molecular mass distribution of the hyperbranchedmethacrylated polyester D-1 analyzed with GPC analysis.

FIG. 7 depicts the dynamic, viscosity of the hyperbranched(meth)acrylated polyester.

FIG. 8 depicts flow time of hyperbranched polyesters and MUP usingviscometric cup.

FIG. 9 depicts curing time and belt speed to tack-free state for UVcured polyester films.

FIG. 10 depicts glass transition temperatures of the cured hyperbranchedpolyesters.

Oligomers with a strongly branched structure are a new family ofpolymers which has been attracting increasing interest for manyapplications, e.g., in agriculture, medicine, cosmetics, adhesives andcoatings. The oligomers are referred to as hyperbranched polyesters witha three-dimensional molecular architecture and possessing starbursttopology (D. A. O'Sullivan, Chem. Eng. News, 20 (1993); D. A. Tomalia,A. M. Naylor, and W. A. Goddard III, Angew. Chem. Int. Ed. Engl., 29,138 (1990). An important structural difference between linear oligomersand hyperbranched polyesters is that a linear oligomer of sufficientmolecular weight contains an entanglement of flexible molecular chains,while a hyperbranched polyester is a compact molecule with many brancheswhich carry a high number of terminal functional groups on eachmolecule.

With the present invention it was found that hyperbranched polyesterswith reactive acrylate double bonds at chain extremities can be used toreduce viscosity, increase reaction rate, and improve adhesion tosubstrates due to their very special molecular structures. This new kindof molecules modifies the physical and chemical properties both is ofthe resin system and of the final product after curing, therebyfacilitating their use in coating and adhesive systems. Further, withthe present invention hyperbranched polyesters with high molecularweight can be obtained in a simple process from readily available andinexpensive raw materials.

Hyperbranched polyester research is still fairly new, and to date nocommercial products are available. The main difficulties in preparingthree-dimensional and ordered hyperbranched polyesters are preservingthe regularity and order in the structures, characterization of theproducts, and separating the products from the excess of reactants.Little work has been performed to prepare adhesive and coating systemswith hyperbranched polyesters, especially for radiation curingapplications. A series of work on allyl ether maleate hyperbranchedpolyesters for UV curing coatings have been reported (M. Johansson, E.Malmstrom, and A. Hult, J. Polym. Sci., Part A: Polym.Chem., 31, 619(1993); E. Malmstrom and A. Hult "Hyperbranched polyesters and theirDegree of Branching as Determined by ¹³ C-NMR", Proceedings of NordicPolymer Days 1994.).

With the present invention it has been possible to synthesize a seriesof new hyperbranched (meth)acrylated polyesters with different number ofterminal double bonds per molecule. The rheological properties of theresins prepared from the polyesters and the mechanical properties of UVcured films are improved in a pronounced manner compared with knownpolymers.

Thus, the present invention relates to a hyperbranched polyester of apolyol with 3 to 10 reactive hydroxyl groups, preferably of equivalentreactivity, and an aromatic polycarboxylic anhydride with 2 to 4carboxyl groups, preferably with 3 carboxyl groups,

each hydroxyl group of the polyol forming an ester linkage with oneanhydride group of the polycarboxylic anhydride,

and further glycidyl (meth)acrylate or allyl glycidyl ether formingester linkages with the remaining carboxyl groups of the anhydride andfree hydroxyl groups.

The invention further relates to a hyperbranched polyester as definedabove in which (meth)acrylic anhydride and/or an aliphatic carboxylicanhydride form/s ester linkages with the free hydroxyl groups.

The present invention further relates to a process for the production ofa hyperbranched polyester, and hyperbranched polyester obtainable by theprocess characterized in that it comprises the following steps:

a) reacting an aromatic polycarboxylic anhydride with 2 to 4 carboxylgroups, preferably 3 carboxyl groups, with a polyol with 3 to 10reactive hydroxyl groups, preferably of equivalent reactivity, in thepresence of an activating agent, the amount of anhydride being at leastone mole of anhydride per hydroxyl group in the polyol,

b) reacting the product from a) with glycidyl (meth)acrylate or allylglycidyl ether in an amount at least corresponding to one mole ofglycidyl (meth)acrylate or allyl glycidyl ether per free carboxylic acidgroup of the product of a). The process and the polyester obtainable bythe process can further comprise the following step;

c) the product from step b) is further reacted with (meth)acrylicanhydride in an amount sufficient to esterify a part or all of the freehydroxyl groups of the product from step b). The products from step b)or c) can further be reacted with an aliphatic carboxylic anhydride inan amount to esterify a part of or all of the remaining hydroxyl groupsof the products.

Two principally different methods have been developed for the synthesisof hyperbranched polymers: a convergent growth approach, where growthbegins at the chain ends, and a divergent growth approach, where growthbegins at a central core. In the present invention, the hyperbranchedpolyesters with terminal double bonds were synthesized by controlledstepwise divergent preparation, i.e., the synthesis started at thecentre of the hyperbranched polyester. Two or three steps were needed toobtain hyperbranched polyesters with a predetermined number of terminaldouble bonds located at the surface of the oligomeric sphere. Thereaction scheme for the synthesis of the hyperbranched polyester can beillustrated for a polyol with 4 hydroxyl groups as shown in FIG. 1 (B ishydroxyl groups, and D is unsaturated groups). New nomenclaturedeveloped by K. L. Wooley, J. M. J. Frechet and C. J. Hawker, Polymervol. 35, No. 21, 1994, names the starburst hyperbranched molecule ofFIG. 1 a dendritic polymer.

In the first reaction step an aromatic carboxylic anhydride with 2 to 4carboxyl groups, preferably 3 carboxyl groups, and a polyol with 3 to 10hydroxyl groups and an activating agent were heated to temperaturesabout or below 100° C., preferably initially to 70° to 80° C. andgradually increasing to about 100° C. at the end of the reaction, in thepresence of a solvent and under inert gas atmosphere, preferablynitrogen atmosphere. The aromatic carboxylic anhydride is mostpreferably 1,2,4-benzenetricarboxylic anhydride. suitable polyols areall polyols having 3 to 10 hydroxyl groups and the hydroxyl groups arepreferably of equivalent reactivity, which means that the esterificationof each hydroxyl group will proceed equally easy to start the buildingup of the regular molecule. Examples of such polyols aretrimethylolpropane, pentaerythritol or a dimer thereof, mono- anddisaccharides, with pentaerythritol as a preferred embodiment. Theamount of added anhydride is at least one mole of anhydride per hydroxylgroup of the polyol, but preferably the anhydride is added in an excessamount. An excess of 20-50 mol % is suitable. An activating agent isused to activate the anhydride group. The activating agent is present ina catalytic amount. The activating agent stannous chloride is apreferred embodiment. A suitable solvent is for exampleN,N-dimethylformamide (DMF).

For a product mixture of 1,2,4-benzenetricarboxylic anhydride withpentaerythritol the IR spectrum with residual 1,2,4-benzenetricarboxylicanhydride is shown by curve 1 in FIG. 2. Toluene was used to wash thereaction product to remove the excess of 1,2,4-benzenetricarboxylicanhydride until no peaks at 1760 and 1850 cm⁻¹ for anhydride groupscould be observed, shown as curve 2 in FIG. 2. The wide absorption bandsat the range of 2750 to 3400 cm⁻¹ in the IR spectrum indicate theterminal carboxyl groups on the benzene ring. For this product mixtureeach polyolester of the polycarboxylic acid anhydride has two carboxylend groups. Three isomer products could be obtained in this system, andthe molecular structures are shown in FIG. 3. The product is largely amixture of meta and para isomers of the ester according to the relativereactivity of the anhydride and the carboxyl groups at low reactiontemperature. A small amount of ortho isomer is expected to be ahydrolysis and reesterification product of para and meta polyolesterformed. The reaction of carboxyl and hydroxyl groups is favoured atelevated temperatures.

The polyolester was further reacted with glycidyl (meth)acrylate orallyl glycidyl ether in an amount at least corresponding to one mole ofglycidyl (meth)acrylate or allyl glycidyl ether per free carboxylic acidgroup of the formed polyester, preferably in an excess amount, i.e.about 5 wt %. Glycidyl acrylate is the preferred reactant. The reactionis carried out in a solvent, such as a mixture of DMF and toluene in thepresences of a basic catalyst and an inhibitor for radicalpolymerization until no carboxyl groups could be detected by end-grouptitration. As basic catalysts common bases can be used, but benzyldimethyl amine is preferred. Conventional inhibitors such ashydroquinone is used. The reaction temperature is below 100° C.,preferably about 70° C. The IR spectrum of the product is shown as curve3 in FIG. 2. The appearance of the wide absorption at around 3460 cm⁻¹means the formation of hydroxyl groups on the molecular chains due toreaction of epoxy and carboxyl groups. Finally, residual solvent wasremoved by evacuation at low temperature. The final "starburst"hyperbranched polyester products with double bonds at the end groups aretranslucent viscous liquids with one hydroxyl group at each end group.The molecular structure, when started with pentaerythritol, is ideallysphere-like, with about 8 end-double bonds. The principal formula isshown in FIG. 4.

The hydroxyl groups of the hyperbranched polyester with terminal doublebonds were reacted further by ester formation with (meth)acrylicanhydride in an amount sufficient to esterify a part of or all of thefree hydroxyl groups in order to prepare the hyperbranched polyestermolecules with further end-double bonds. Of the two acrylic anhydrides,the methacrylic anhydride is preferred. The hyperbranched polyesterstarted from pentaerythritol with about 16 end-double bonds with theidealized formula is shown in FIG. 5. The IR spectrum of thehyperbranched polyester with about 16 double bonds is shown by curve 4in FIG. 2. Almost no peak for hydroxyl group could be observed.

In a last step the product with end-double bonds is reacted with analiphatic carboxylic anhydride, preferably acetic anhydride to esterifya part of or all of the remaining hydroxyl groups on the molecularchains for decreasing molecular polarity of the hyperbranched polyester,and improving its compatibility with multifunctional comonomers. Thisesterification can also be made of the hydroxyl groups of thehyperbranched polyester before the previous reaction with (meth)acrylicanhydride, thus omitting the further introduction of (meth)acrylicdouble bonds. The final hyperbranched polyester products with terminaldouble bonds after modifying, prepared in the present invention arefairly transparent colourless viscous liquids. As shown in FIGS. 4 and 5the double bonds are in end groups, located at the surface of theoligomeric sphere, which is highly favourable for UV cure.

The polydispersity measured by GPC analysis (FIG. 6) varied from 1,4 to1,9 at different reactant ratios and reaction temperatures withmolecular weights of maximum 2500 obtained, which corresponds to amodified polyester molecule with four main branches. The wide molecularweight distribution is mainly attributed to incomplete reaction between1,2,4-benzenetricarboxylic anhydride and pentaerythritol, hyperbranchedpolyester fragmentation during hyperbranched polyester growth, and tothe small excess of glycidyl (meth)acrylate monomer which react furtherwith by-products in the system, responsive to UV irradiation.

The hyperbranched polyester according to the invention can be used ascurable resins. The resins are preferably cured by UV or EB radiationand most preferably by UV radiation. The resins have lower viscositythan known oligomer resins and can be used without a comonomer or withlower amounts of comonomer than for conventional oligomer resins. The UVcuring of the resin according to the invention is very rapid, down toparts of a second at room temperature operation. This means a high speedof cure and low energi consumption. The obtained products have a highglass transition temperature, resulting in products of high hardness,for example coatings or laminates with high surface hardness.

The resins are solvent free and can be prepared from 100% of thehyperbranched polyester according to the invention. The resins canhowever, also comprise multifunctional monomers. A suitable amount ofcomonomer is 5-20 wt % and the rest 80-95 wt % being the hyberbranchedpolyester. The resins preferably comprise a photofragmenting initiator.The amount of photofragmenting initiator used is in the range 1-5 wt %based on the resin. Conventional photofragmenting initiators can be usedand a preferred initiator is benzoyl dimethylketol. As multifunctionalmonomers compounds with reactive double bonds can be used, such astrimethylolpropane tri(meth)acrylate, hexandiol diacrylate,trimethylolpropane triallylether, pentaerythritol tri/tetra-allylether,triallylcyanurate, trimethylolpropane triacrylether, pentaerythritoltetraacrylether. Trimethylolpropane triacrylate being a preferredembodiment.

The resin according to the invention can be used in many differentfields of which could be mentioned coatings, adhesives, laminates, foilsand thin films and fibre-reinforced composites.

The invention will now be illustrated with the following examples whichhowever, are not intended to restrict the invention. with parts andpercent are meant parts per weight and weight-%, if nothing else ismentioned.

The following chemicals are used:

Pentaerythritol PETL!

1,2,4-Benzenetricarboxylic Anhydride BTCA!

Glycidyl Acrylate GA!

Methacrylic Anhydride MAA!

Acetic Anhydride AA!

Stannous Chloride SC!

Benzyldimethylamine BDMA!

Hydroquinone HQ!

Dimethyl Formamide DMF!

Trimethylolpropane Triacrylate (TMPTA)

Benzoyldimethylketol (BDK)

EXAMPLE 1

92.2 g (0.48 mol) BTCA is dissolved in 100 ml DMF at 80° C. 10.9 g (0.08mol) PETL and 0.1 g (0.1 wt %) SC are added, and the solution is kept at80° C. for 8 hours, and then heated to 100° C. for 10 hours under N₂.Most of DMF is distilled off in vacuum and toluene is poured into theproduct to dissolve the residual BTCA. The product is washed withtoluene until no BTCA is detected in IR spectra (1760 and 1850 cm⁻¹ foranhydride groups). 57.2 g polyolester is obtained, as a white powder,with the yield of about 79% after completely removing the solvents. Theacid number of 475 mg KOH/g polyester is determined by titration with0.1N KOH. 65.09 g (0.508 mol with a 5% excess) GA is added slowly dropby drop at 70° C. together with 5 g (2.5%) BDMA as catalyst and 1000 ppmHQ as inhibitor, dissolved in 70 ml DMF. After 7 hours at 70° C. nocarboxyl groups can be detected by titration. DMF is distilled off invacuum. The product is a viscous liquid with maximum 8 acrylate and 8hydroxyl groups per molecule. This product is called D-1OH.

12.4 g (0.121 mol) AA is added to 40.8 g D-1OH in 50 ml DMF which reactswith about 6 hydroxyl groups per molecule (averaged about 2 OH groupsper molecule remain). The product solution is then heated for 2 hours at70° C. and DMF is distilled off in vacuum. The obtained product, calledD-1, is a viscous liquid with about 8 acrylate groups and 2 hydroxylgroups per molecule.

EXAMPLE 2

40.8 g D-1OH is dissolved in 50 ml DMF with 500 ppm HQ and 12.4 g (0.08mol) MAA and 4.1 g (0.04 mol) AA are added slowly, drop by drop at 70°C. for two hours to react with the hydroxyl groups. DMF is removed byvacuum distillation. The product, called D-2, is a viscous liquid withabout 12 (meth)acrylate groups and 2 hydroxyl groups per molecule.

EXAMPLE 3

40.8 g D-1OH is dissolved in 50 ml DMF with 500 ppm HQ as inhibitor.24.8 g MAA (0.161 mol) is added and heated to 70° C. After 2 hours thereaction is complete. DMF is removed by vacuum distillation. Theproduct, called D-3, is a viscous liquid with about 8 acrylate and 8methacrylate groups per molecule.

The dynamic viscosity for the products from Examples 1 to 3 was measuredas a function of frequency for the hyperbranched polyesters withdifferent numbers of double bonds, as shown in FIG. 7. The hyperbranchedpolyester D-1OH, according to Example 1, with about 8 double bonds andwithout acetic anhydride modification, has the highest viscosity due tothe many hydroxyl groups in the system, resulting in intermolecularhydrogen bonding (hyperbranched polyester aggregation). At decreasinghydroxy functionality, the dynamic viscosities of the hyperbranchedpolyester largely decrease in order of D-1, D-2 and D-3, according toExamples 1 to 3, at lower frequency. D-3 has the lowest viscositycompared with D-1 and D-2 because of the high number of double bonds (noremaining hydroxyl groups) at the surface of the spherical molecule.This results in increasing symmetry of the hyperbranched molecule, apartfrom less influence from the hydrogen bonding.

Low viscosity is particularly important in controlling the levellingtime of a coating and for evaluation of the processability of aradiation curable coating and adhesive. This is especially the case for100% solid coating systems for thin films. The oligomer is the principalconstituent and primarily responsible for the basic properties of thecoating. The viscosity of the oligomer is, therefore, an importantparameter since it determines the amount of oligomer required in thefinal product. For control of the viscosity of the radiation curableresin there are only two parameters, namely the viscosity of theoligomer and the amount of comonomer added.

The principal rheological difference between the branched and the linearpolyester molecules lies in the smaller spatial extension of thebranched molecule at a given molecular mass. The viscosity of the resinis related to the dynamic extension in space and the segment densitywithin the volume of the molecule. Therefore, the sphere-like starburst(meth)acrylated polyester according to the invention has lower viscositythan the linear polyester.

Flow time measurements are another evaluation of the relative viscosityof various coatings and adhesives, using a viscosimetric cup. Theviscosities of the hyperbranched (meth)acrylated polyesters containing15 wt % trimethylolpropane triacrylate (TMPTA), as comonomer and aconventional epoxy acrylate modified unsaturated polyester (MUP)containing 35 wt % TMPTA at 21° C. are compared in FIG. 8. It can beseen that the flow times through the viscosimetric cup for hyperbranchedpolyester resins are much shorter than for MUP resin. This means thatthe viscosity of MUP is much higher than that of hyperbranchedpolyester. A practical consequence is that the processability ofhyperbranched polyester containing resins is improved due to lowerviscosity.

EXAMPLE 4

3 parts of BDK were dissolved in 100 parts of a mixture of 15% by weightof TMPTA and 85% by weight of D-1, D-2 or D-3, the resultant resins werecoated on a polyethylene terephtalate (PET) sheet. The test samples werecured in air on a conveyer belt with variable speed by UV irradiationfor 0,15 seconds under a 300 W/in (120 W/cm) Model F300 D bulb (FusionUV Curing Systems) in the exposure chamber.

EXAMPLE 5

The procedure of Example 4 was repeated except that 100 parts of D-1,D-2 or D-3 polyesters are used instead of the mixture of the polyestersand TMPTA.

The irradiation time is varied by changing the speed of the conveyorbelt. The polymerization rate of the hyperbranched polyester resins wasdetermined by measuring the irradiation time required to obtain fullytack-free state for the cured film using a cotton bar. The data aregiven in FIG. 9. The resin with oligomer D-3 needs the shortest curingtime to get tack-free state.

The glass transition temperatures of the crosslinked (meth)acrylatedhyperbranched polyesters D-1, D-2 and D-3 according to Example 5 fromDynamic Mechanical Thermal Analysis (DMTA) measurements are given inFIG. 10. It can be seen that the glass transition temperature increasesrapidly with increasing functionality of the cured hyperbranchedoligomer.

The physical properties of the cured material are related to thestructure of the crosslinked network. The glass transition temperature,T_(g), is a function of the flexibility of the polymeric chains. If theflexibility decreases, the transition temperature increases. Flexibilityis a function of chain structure, crosslinked structure and crosslinkdensity. For the hyperbranched polyesters the spherical shape of themolecules and the high crosslink density due to its high functionalitydecreases the flexibility of the cured films. Therefore, crosslinkedhyperbranched polyester give higher glass transition temperature thancrosslinked linear oligomers as an effect of the structural difference.

The measurements made in the present invention were performedaccordingly:

Molecular Weight Distribution

Measurements of molecular weight distribution were performed on a WATERS410 GPC system equipped with a WISP 712 automated injector. The columnsused were μ-Styragel of pore sized: 500, 10⁵, 10⁴, 10³, and 100 Ångstromwith polystyrene standards for calibration and tetrahydrofuran (THF) assolvent.

Dynamic Mechanical Spectroscopy

The dynamic mechanical properties of the hyperbranched polyesters weremeasured by shear rheometry (Dynamic Analyser RDAII). Viscous liquidsamples were examined at 25° C. using two parallel plates of 12.5 mmradius with 0.62 to 0.76 μm gap over a wide range of frequencies.

Flow Time

Flow time of the resins with multifunctional monomer added was measuredusing a viscometric cup of number 68 for comparison of the viscosity ofthe hyperbranched polyesters with that of modified linear unsaturatedpolyester.

IR spectra

Infra-red spectra of the polyesters at different reaction stages wererecorded on a Perkin-Elmer Model 1710 Fourier Transform Spectrometerprepared as pressed KBr solid disk or smeared as an acetone solution ofthe resin on a NaCl prism to form a thin film.

Thermomechanical analysis

Dynamic Mechanical Thermal Analyser (DMTA, Polymer Laboratories MK II)was used to measure glass transition temperature (T_(g)) at the range of40° to 250° C. and 1 Hz frequency of completely UV cured films withoutTMPTA added.

We claim:
 1. Hyperbranched polyester of a polyol with 3 to 10 reactivehydroxyl groups, and an aromatic polycarboxylic anhydride with 2 to 4carboxyl groups,each hydroxyl group of the polyol forming an esterlinkage with one anhydride group of the polycarboxylic anhydride, andfurther glycidyl (meth)acrylate or allyl glycidyl ether forming esterlinkages with the remaining carboxyl groups of the anhydride and freehydroxyl groups.
 2. Hyperbranched polyester of a polyol with 3 to 10reactive hydroxyl groups and an aromatic polycarboxylic anhydride with 2to 4 carboxyl groups,each hydroxyl group of the polyol forming an esterlinkage with one anhydride group of the polycarboxylic anhydride, andglycidyl (meth)acrylate or allyl glycidyl ether forming ester linkageswith the remaining carboxyl groups of the anhydride and free hydroxylgroups, and further an anhydride selected from the group consisting of a(meth)acrylic anhydride, an aliphatic carboxylic anhydride, and blendsthereof, forming ester linkages with the free hydroxyl groups. 3.Hyperbranched polyester produced by a process comprising the followingsteps:a) reacting an aromatic polycarboxylic anhydride with 2 to 4carboxyl groups with a polyol with 3 to 10 reactive hydroxyl groups inthe presence of an activating agent, the amount of anhydride being atleast one mole of anhydride per hydroxyl group in the polyol, b)reacting the product from a) with glycidyl (meth)acrylate or allylglycidyl ether in an amount at least corresponding to one mole ofglycidyl (meth)acrylate or allyl glycidyl ether per free carboxylic acidgroup of the product of a).
 4. The hyperbranched polyester according toclaim 3, wherein the activating agent is present in a catalytic amount.5. The hyperbranched polyester according to claim 3, wherein theactivating agent is SnCl₂.
 6. The hyperbranched polyester of claim 3,the process further comprising c) reacting the product from step b) with(meth)acrylic anhydride in an amount sufficient to esterify at least apart of the free hydroxyl groups of the product from step b).
 7. Thehyperbranched polyester of claim 3, the process further comprising c)reacting the product from step b) with an aliphatic carboxylic anhydridein an amount sufficient to esterify at least a part of the remaininghydroxyl groups of the product.
 8. The hyperbranched polyester of claim1 wherein the reactive hydroxyl groups of the polyol have equivalentreactivity and the aromatic polycarboxylic anhydride has three carboxylgroups.
 9. The hyperbranched polyester of claim 2 wherein the reactivehydroxyl groups of the polyol have equivalent reactivity and thearomatic polycarboxylic anhydride has three carboxyl groups.
 10. Thehyperbranched polyester of claim 3 wherein the reactive hydroxyl groupsof the polyol have equivalent reactivity and the aromatic polycarboxylicanhydride has three carboxyl groups.
 11. The hyperbranched polyester ofclaim 6, the process further comprising reacting the product from stepc) with an aliphatic carboxylic anhydride in an amount sufficient toesterify at least a part of the remaining hydroxyl groups of theproduct.
 12. The process of claim 11, wherein the aromaticpolycarboxylic anhydride has three carboxyl groups and the reactivehydroxyl groups of the polyol have equivalent reactivity.
 13. Theprocess according to claim 12, further comprising the following step:c)reacting the product from step b) with (meth)acrylic anhydride in anamount sufficiently to esterify at least a part of the free hydroxylgroups of the product from step b).
 14. The hyperbranched polyesteraccording to any one of claims 2, 6, 7, 9, or 11, wherein the(meth)acrylic anhydride is (meth)acrylic anhydride and the aliphaticcarboxylic anhydride forming ester linkages with the free hydroxylgroups in acetic anhydride.
 15. The hyperbranched polyester according toany one of claims 1 to 7, wherein the polyol is pentaerythritol and thearomatic polycarboxylic anhydride is 1,2,4-benzenetricarboxylicanhydride and the glycidyl (meth)acrylate is glycidyl acrylate.
 16. Thehyperbranched polyester according to any one of claims 1, 2, 3, 4, 5, 6,7, 8, 9, 10 or 11, wherein the hyperbranched polyester is a dendriticpolyester or a crosslinked dendritic polyester.
 17. A process for theproduction of a hyperbranched polyester, said process comprising thesteps of:a) reacting an aromatic polycarboxylic anhydride with 2 to 4carboxyl groups with a polyol with 3 to 10 reactive hydroxyl groups inthe presence of an activating agent, the amount of anhydride being atleast one mole of anhydride per hydroxyl group in the polyol, b)reacting the product from a) with glycidyl (meth)acrylate or allylglycidyl ether in an amount at least corresponding to one mole ofglycidyl (meth)acrylate or allyl glycidyl ether per free carboxylic acidgroup of the product of a).
 18. The process according to claim 17,wherein the activating agent is present in a catalytic amount.
 19. Theprocess according to claim 17, wherein the activating agent is SnCl₂.20. The process according to claim 17, wherein the reaction mixture ofstep a) is heated to a temperature below 100° C.
 21. The processaccording to claim 17, wherein the amount of anhydride in step a) is atleast 1.2 moles per hydroxyl group and the amount of glycidyl(meth)acrylate or allyl glycidyl ether in step b) is at least 1.05 molesper free carboxylic acid group.
 22. The process according to claim 17,wherein the reaction of step b) is carried out in the presence of abasic catalyst and an inhibitor for radical polymerization.
 23. Theprocess according to claim 22, wherein the basic catalyst isbenzyldimethyldiamine.
 24. The process according to claim 17, furthercomprising the following step:c) reacting the product from step b) with(meth)acrylic anhydride in an amount sufficient to esterify at least apart of the free hydroxyl groups of the product from step b).
 25. Theprocess according to claim 24, wherein the anhydride is methacrylicanhydride.
 26. The process according to any one of claims 17, 24, 12, or13, further comprising reacting the product from step b) or c) with analiphatic carboxylic anhydride in an amount sufficient to esterify atleast a part of the remaining hydroxyl groups of the product.
 27. Theprocess according to claim 26, wherein the aliphatic carboxylicanhydride is acetic anhydride.
 28. The process according to any one ofclaims 17 to 25, wherein the polyol is pentaerythritol and the aromaticpolycarboxylic anhydride is 1,2,4-benzene-tricarboxylic anhydride andthe glycidyl (meth)acrylate is glycidyl acrylate.
 29. The processaccording to any one of claims 17 to 25, wherein the hyperbranchedpolyester is a dendritic polyester or a crosslinked dendritic polyester.30. The curable resin comprising the hyperbranched polyester of any oneof claims 1 to
 7. 31. The curable resin according to claim 30, furthercomprising a photofragmenting initiator.
 32. The curable resin accordingto claim 31, further comprising a multifunctional monomer.
 33. Thecurable resin according to claim 32 wherein the multifunctional monomeris trimethylolpropane triacrylate.
 34. The curable resin according toclaim 30 wherein the resin is curable with UV irradiation.
 35. Theprocess according to claim 12, wherein the activating agent is presentin a catalytic amount.
 36. The process according to claim 12, whereinthe activating agent is SnCl₂.
 37. The process according to claim 12,wherein the reaction mixture of step a) is heated to a temperature below100° C.
 38. The process according to claim 12, wherein the amount ofanhydride in step a) is at least 1.2 moles per hydroxyl group and theamount of glycidyl (meth)acrylate or allyl glycidyl ether in step b) isat least 1.05 moles per free carboxylic acid group.
 39. The processaccording to claim 12, wherein the reaction of step b) is carried out inthe presence of a basic catalyst and an inhibitor for radicalpolymerization.
 40. The process according to claim 39, wherein the basiccatalyst is benzyldimethyldiamine.
 41. The process according to claim13, wherein the anhydride is methacrylic anhydride.
 42. A coating,adhesive, laminate, foil, thin film, or fiber-reinforced compositecomprising a cured product of the curable resin of claim 30.